Pinched-off, resealed nerve terminals (synaptosomes) will serve as an in vitro model system for a multidisciplinary study of mammalian CNS presynaptic nerve terminal function. The following aspects of synaptosome function will be investigated: 1. Calcium buffering by intra-terminal organelles. Ca uptake studies and electron microscopic identificaton of Ca sequestration sites will be used to test the hypothesis that the smooth endoplasmic reticulum plays a critical role in buffering the Ca that enters terminals during activity. 2. Potassium permeability. We will study the properties of a K flux that is increased by depolarization, and blocked by tetraethylammonium ions and aminopyridines. 3. Distribution and transport of chloride, protons and magnesium across the plasmalemma. We will try to determine how these ions are transported across the plasmalemma, and whether or not they are distributed at equilibrium, across the plasmalemma. We would also like to determine whether or not Mg is sequestered in intra-terminal organelles. 4. The relationship between Ca entry and transmitter release. There are two pathways of Ca entry, one of which inactivates; we will try to determine how transmitter (e.g. catecholamine) release correlates with the two modes of Ca entry. 5. Transmitter re-uptake mechanisms. The role of Cl - in the Na-dependent uptake of GABA will be investigated. 6. Synaptic modulation. The effects of various neurotransmitters will be tested on the presynaptic terminals. We hope to determine whether or not the transmitters affect the properties of various ion-specific (Ca and K) channels in the terminals.